Elastic behavior of transforming and nontransformingV3Si

The differences in the shear modulus and its isothermal pressure derivative for transforming and nontransforming crystals of ${\mathrm{V}}_3$Si are explained in terms of a larger number of defects in the nontransforming samples. The defects give rise to microdomains of tetragonal distortions which stiffen the lattice for shear-type motion. The estimated defect concentration is consistent with the vacancy model proposed recently to explain the discrepancy between the sound-velocity and lattice-constant measurements for ${\mathrm{V}}_3$Si as a function of pressure. The estimated ratio of vacancies in transforming and nontransforming variety agrees well with the ratio of the measured residual-resistivity ratios in these compounds.